1. Field of the Invention
The present invention pertains to a device for zone-by-zone tensioning of a flaccid, flat material, and especially to an embroidery hoop for textiles.
2. Description of the Related Art
It is known that such a device can be equipped with an annular tensioner that has a member that can be filled by a gas or fluid and which tensions and clamps the flaccid material by increasing its diameter. In particular, it is known that the diameter of the member that can be filled by a gas or fluid is increased by increasing the pressure, thus tensioning the flaccid material, and clamping it relative to a rigid hoop arranged on the outside. It is also known that such a device can be equipped with two rings, one of which can be filled by a gas or fluid or has a member that can be filled by a gas or fluid (see Japanese publication JP-AS Sho-54-23632).
Embroidery hoops have become known which consists essentially of two circular, concentric assembly groups, the inner one of which is formed by a circular bellows with a support ring arranged in it, while the outer one is formed by another circular ring, whose internal diameter is slightly larger than the external diameter of the nonfilled bellows. The edge of the zone to be tensioned is pulled through the circular gap thus formed. Pumping up the bellows increases its external diameter, as a result of which the edge of the material is clamped against the outer ring. Such devices facilitate automation by performing the operations for clamping the textile material, which were previously necessary, by means of a computer-controlled pneumatic system (see Japanese publication JP-AS- Sho-54-23633).
However, the state of the art known from these documents has the disadvantage that the material cannot be pulled tightly enough and that it must be tensioned even prior to clamping.
Fabricating the ring-shaped bellows takes a disadvantageously great amount of effort. Along with the low lot numbers to be produced, it makes them very expensive. In addition, users complain that the tensioned material is still too loose for embroidering.
An embroidery hoop for zone-by-zone tensioning of a flaccid, flat textile material, which is known from U.S. Pat. No. 1,524,732, has a tensioning member which can be placed on the material and is designed as a comb of oval cross section equipped with needles on the lower side, which comb is wedged with locking barbs on the inside of a hoop part, thus being held in its position extending upward from the hoop part.
This also results in it being impossible to simultaneously tension the material to be embroidered on the long sides and the transverse sides, because the combs on the long sides are located outside the available width of passage for the material to be embroidered, so that all-around clamping of the material to be embroidered is ruled out.
Concerning the function of the needle-equipped comb, it is explained in U.S. Pat. No. 1,524,732 that the needles are provided for catching the material to be embroidered, and that when the comb is introduced under the ends of the locking barbs, the material to be embroidered, when held in the same way on the opposite side, tends--due to the oval shape of the comb--to bring about a movement of the comb toward the opposite side of the hoop, as a result of which the locking barbs are locked in their supports. A separate drive for rotating the comb or combs is not provided.
Concerning the function, it is also explained that when the material to be embroidered passes through the space between the top side of the hoop and the lower part of the comb, the comb tends to rotate, and that rotation ends when the needles touch the top side of the hoop. The needles now penetrate the material to be embroidered, thus damaging it.
The rotation takes place during a pull on the material to be embroidered, which pull is directed away from the comb, to tension the material. However, the pulling movement directed away from the comb detaches the comb arranged on the opposite side from the material to be embroidered, so that the material to be embroidered must be constantly kept under tension to tension it and to keep it tensioned. This pulling force must be exerted when the material to be embroidered is moved, corresponding to the embroidery pattern, together with the hoop under the embroidering tools.
When two opposite combs are used, the pulling force on the material to be embroidered must always be directed away from the combs in order to rotate the combs and consequently to cause the needles to penetrate into the material to be embroidered, as a result of which the material to be embroidered would be pulled toward the center of the hoop and a so-called slack would form, so that the opposite of tensioning would be achieved.